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    SubjectRe: [RFC PATCH 0/6] Do not call ->writepage[s] from direct reclaim and use a_ops->writepages() where possible
    On Tue, Jun 08, 2010 at 10:28:14AM +0100, Mel Gorman wrote:
    > > - we also need to care about ->releasepage. At least for XFS it
    > > can end up in the same deep allocator chain as ->writepage because
    > > it does all the extent state conversions, even if it doesn't
    > > start I/O.
    > Dang.
    > > I haven't managed yet to decode the ext4/btrfs codepaths
    > > for ->releasepage yet to figure out how they release a page that
    > > covers a delayed allocated or unwritten range.
    > >
    > If ext4/btrfs are also very deep call-chains and this series is going more
    > or less the right direction, then avoiding calling ->releasepage from direct
    > reclaim is one, somewhat unfortunate, option. The second is to avoid it on
    > a per-filesystem basis for direct reclaim using PF_MEMALLOC to detect
    > reclaimers and PF_KSWAPD to tell the difference between direct
    > reclaimers and kswapd.

    I went throught this a bit more and I can't actually hit that code in
    XFS ->releasepage anymore. I've also audited the caller and can't see
    how we could theoretically hit it anymore. Do the VM gurus know a case
    where we would call ->releasepage on a page that's actually dirty and
    hasn't been through block_invalidatepage before?

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